Background & Rationale
Why have streambank failures been treated with rocks, concrete and steel if the benefits of having a healthy riparian area are known?
In 2013, Alberta experienced a heavy rainfall that was considered the worst in its history and the damage was over C$5 billion.[1]
After that event, many measures have been taken and studied to prevent and mitigate damages from flooding. The health of riparian area was one of the many that had its importance raised because of the protection against flood damages. Then, a comprehensive survey about the health of riparian area began in 2015 and this data was used in this work to evidence what causes are related to an unhealthy riparian area and what is the contribution of conventional treatments of streambank failures.
After that event, many measures have been taken and studied to prevent and mitigate damages from flooding. The health of riparian area was one of the many that had its importance raised because of the protection against flood damages. Then, a comprehensive survey about the health of riparian area began in 2015 and this data was used in this work to evidence what causes are related to an unhealthy riparian area and what is the contribution of conventional treatments of streambank failures.
A healthy riparian zone prevents excessive erosion, stabilize riverbanks, slow floodwaters through natural floodplains, improve water quality, provide habitat for fish and wildlife and offer aesthetic, recreational and economic benefits.[2][3][5][6][10][11][18][24][25]
The streambank is part of the riparian zone and it is also the interface between water channel and land. A stable streambank holds its soil and also avoid other sediments from run-off into the stream.[3] [4] [5][6] The other effect on streambanks is the fact that the plants, especially the ones with the deep root system, dissipate more energy from the water flow and allows the soil release slowly the overflow from storm events. [2][3][5][6] |
Current treatments for riparian zone
The anti-flood studies aimed also the way riparian areas have been rehabilitated in case of streambank failure, comparing conventional engineering (with rocks, concrete, steel such as rip-rap and landfill with grass) and soil bioengineering (with plants and other supporting materials).
Conventional engineering has been used to stabilize river banks due to varied circumstances.[3] Urban and urbanized environment have limited riparian buffer because of the presence of infrastructure components on the ground and underground such as edification, roads, pipelines etc. Because of the limited space to perform recovery works on streambank failures, conventional engineering solutions have been adopted frequently once they are standardized and have predictable behaviour. On the other hand, those modifications made by people significantly alter the movement and storage of water that is important to the riparian system. A channelized or partially channelized stream no longer allows the dissipation of energy on riparian vegetation, leaving the water flow with more energy, then causing erosion along the stream and also flooding problems. [2][3][4][5][6][7][8] Not only in Alberta, the health of riparian zone related to flooding damages is an important concern in other populated regions.
Conventional treatments for streambanks - Grass then Rip-Rap
Covering streambanks with grass after bank recovery has been a common practice in infrastructure works and it has been showing that this is not an effective treatment for streambanks in long-term due to erosive processes.
Rip-rap is another common treatment for bank failures, especially when landfill with grass fails because it presents lower cost and provides stability to the bank. It is important to notice that this treatment affects the fish habitat once the rocks are also placed into the water. Choosing this treatment prioritizes the bank stabilization (with rocks interlocking each other) however jeopardizes the other aspects such as hydrodynamics or ecological side of a river bank, losing fish and other species habitat.
Soil bioengineering
Soil bioengineering or only bioengineering in this context is a technique that might modify this paradigm that has been leading to a vicious cycle of riparian degradation. The USDA (2000) defines Bioengineering as the use of living and nonliving plant materials in combination with natural and synthetic support materials for slope stabilization, erosion reduction, and vegetative establishment, and it is most commonly used to stabilize landslide in prone areas and streambanks. However, there is a lack of geotechnical engineering and hydrological design criteria to determine where bioengineering is appropriate in urban and urbanized areas. Therefore, this casts doubts on its effectiveness and causes reluctance in approval or design for engineering projects that include this technique. [13][14][15][16][17][26]
Intuitively or by experience from long ago, one popular method of Bioengineering in Alberta has been deep willow stakes to recover riparian zones by adding long-term strength to soil matrix and change the flow hydrodynamics, influencing riverbank erosion, and consequently protecting the source water. Revegetation of streambanks is commonly used as best practice for restoring riparian corridors and managing streambank erosion, but not often for treating bank failure or toe erosion, due to the lack of consistent numbers for this specific use. Riparian and aquatic vegetation have an interdependence related to river hydrodynamics, sediment transport and morphology. [11][12][13][14][15][16][17][19][20][21][22] This has important implications, such as managing hydraulic roughness for flood control, and maintaining stream bed and bank stable during extreme hydrologic events to prevent damage to property and critical infrastructure, besides the ecological effects in aquatic habitats. [3][4][5][6][7][8][24][25][26]
Intuitively or by experience from long ago, one popular method of Bioengineering in Alberta has been deep willow stakes to recover riparian zones by adding long-term strength to soil matrix and change the flow hydrodynamics, influencing riverbank erosion, and consequently protecting the source water. Revegetation of streambanks is commonly used as best practice for restoring riparian corridors and managing streambank erosion, but not often for treating bank failure or toe erosion, due to the lack of consistent numbers for this specific use. Riparian and aquatic vegetation have an interdependence related to river hydrodynamics, sediment transport and morphology. [11][12][13][14][15][16][17][19][20][21][22] This has important implications, such as managing hydraulic roughness for flood control, and maintaining stream bed and bank stable during extreme hydrologic events to prevent damage to property and critical infrastructure, besides the ecological effects in aquatic habitats. [3][4][5][6][7][8][24][25][26]
Hybrid or Bio-conventional?
Planting few species in a conventional engineering treatment is common as well, for example, vegetated rip-rap [3][4]. There are some variations of conventional engineering where some species are planted with the intention of providing the benefits of a riparian zone, but the results are questionable. The US Army Corps of Engineers policy generally prohibits trees on levees because they can destabilize levees and make it harder to inspect them or get to them in a flood.
Therefore, mixed types of treatment present a potential to have a conventional engineering treatment jeopardized with environmentally innocuous components. This is due to a lack of parameters of, for example, how many species have to be planted per area to provide benefits of a riparian zone.
Therefore, mixed types of treatment present a potential to have a conventional engineering treatment jeopardized with environmentally innocuous components. This is due to a lack of parameters of, for example, how many species have to be planted per area to provide benefits of a riparian zone.
Why are Deep-rooted plants important?
The importance of a proper coverage by deep-rooted plants in a streambank area is already known by the scientific community, but it is still a question mark for contractors and project designers for infrastructure works. [3][4][5][7][8] Plants with deep root systems are the main component of a riparian area and they protect the streambanks from excessive fluvial erosion. Most trees, shrubs, and native grasses will serve this function besides trapping sediments to build and restore banks.
Human activities such as forest harvesting or excessive grazing can reduce or eliminate the amount of deep-rooted vegetation present on the banks providing aquatic habitats, thereby reducing the ability of the banks to withstand erosion through fluvial action. When the sediment load in a channel is increased, banks can be further eroded as the channel widens in order to deliver the sediment-laden flow downstream. Falling, yarding, windthrow, and trampling by large animals can also directly crush, collapse, shear, or otherwise damage stream banks.
Therefore, as deep-rooted plants grow, such as willows in Alberta, and encroaches on the stream, overhanging banks develop because the root mat is strong enough to be “cantilevered” out over the stream when stream flows erode the soil out from underneath.
Human activities such as forest harvesting or excessive grazing can reduce or eliminate the amount of deep-rooted vegetation present on the banks providing aquatic habitats, thereby reducing the ability of the banks to withstand erosion through fluvial action. When the sediment load in a channel is increased, banks can be further eroded as the channel widens in order to deliver the sediment-laden flow downstream. Falling, yarding, windthrow, and trampling by large animals can also directly crush, collapse, shear, or otherwise damage stream banks.
Therefore, as deep-rooted plants grow, such as willows in Alberta, and encroaches on the stream, overhanging banks develop because the root mat is strong enough to be “cantilevered” out over the stream when stream flows erode the soil out from underneath.
Research objectives
The objective of this work is to answer the following questions:
- What are the main factors involved between properly functioning riparian area and not properly functioning?
- How do conventional treatments for streambank failures contribute for riparian health?
- Is bioengineering a more adequate treatment?
Expected Results
A guidance for monitoring and rehabilitation of riparian zones is expected from the results. In other words, it could be possible to adequate the use of conventional treatment, bioengineered or even a hybrid. Therefore, manager, designers or public administrators could discard inappropriate ones and avoid misuses.
References
[1]
"Wikipedia - 2013 Alberta floods," [Online]. Available: https://en.wikipedia.org/wiki/2013_Alberta_floods. [Accessed 30 03 2018].
[2]
"USDA - Natural Resources Conservation Service," [Online]. Available: https://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/technical/?cid=nrcs143_014199. [Accessed 22 March 2018].
[3]
City of Calgary, "Design guidelines for erosion and flood control projects for streambank and riparian stability restoration," 2012.
[4]
Government of Alberta - Transportation, "Erosion and sediment control manual," June 2011. [Online]. Available: http://www.transportation.alberta.ca/4626.htm.
[5]
USDA/NRCS, Streambank soil engineering - Technical supplement 14I - Part 654 (Stream restoratio design) of National Engineering Handbook, USA, 2007.
[6]
A. Stokes, J. Norris, L. Van Beek, T. Boggard, E. Camerrat, S. Mickovski, A. Jenner, A. Di Iorio and T. Fourcaud, "How vegetation reinforces soil on slopes," in Slope stability and erosion control: ecotechnological solutions, Springer, 2008, p. 290.
[7]
D. Gray and R. Sotir, Biotechnical and soil bioengineering - slope stabilization - a practical guide for erosion control, NEW YORK: John Wiley & Sons, Inc., 1996.
[8]
N. J. Coppin and I. G. Richards, Use of Vegetation in Civil Engineering, London: CIRIA, 1990.
[9]
F. Giadrossich, M. Schwarz, D. Cohen, A. Cislaghi, V. C., H. T., C. Phillips and A. Stokes, "Methods to measure the mechanical behaviour of tree roots: A review," 2017.
[10]
H. Schiechtl, Bioengineering for land reclamation and conservation, MUNICH: UNIVERSITY OF ALBERTA, 1980.
[11]
D. Polster, "Natural processes and restoration of drastically disturbed sites," Polster Environmental Services LTD., 2015.
[12]
H. Chang, Fluvial Processes in River Engineering, 1988.
[13]
N. Bankhead, R. Thomas and A. Simon, "A combined field, laboratory and numerical study of the forces applied to, and the potential for removal of, bar top vegetation in a braided river," Earth Surf. Process. Landforms 42, 439–459 (2017), 2017.
[14]
M. Da Liu and R. Williams, "Flow Hydrodynamics across Open Channel Flows with Riparian Zones: Implications for Riverbank Stability," Water, 2017.
[15]
E. Yager and M. Schmeeckle, "The influence of vegetation on turbulence and bed load transport," JOURNAL OF GEOPHYSICAL RESEARCH: EARTH SURFACE, VOL. 118, 1585–1601, 2013.
[16]
N. Pollen and A. Simon, "Estimating the mechanical effects of riparian vegetaion on stream bank stability using fiber bundle model," 2005.
[17]
T. Wu, W. Mckinnell and D. Swanson, "Strength of Tree Roots and landsides on Prince of Wales Island, Alaska," 1978.
[18]
L. Waldron and S. Dakessian, "Soil reinforcement by roots: calculation of increased soil shear resistance from root properties," 1981.
[19]
T. Endo, "Effect of Tree Roots upon the Shear Strength of Soil.," 1980.
[20]
R. Hidalgo, F. Kun and H. Herrmann, "Bursts in a fiber bundle model with continuous damage," PHYSICAL REVIEW E, VOLUME 64, 066122, 2001.
[21]
S. Mickovski and P. Van Beek, "Root morphology and effects oon soil reinforcement and slope stability of young vetiver (Vetiveria zizanoides) plants grown in semi-arid climate.," 2009.
[22]
USDA - FOREST SERVICE, "Soil Bioengineering: An Alternative for Roadside Management.," 2000.
[23]
Government of Alberta, "Guide to the Common Native Trees and Shrubs of Alberta," 2014.
[24]
CANADIAN COUNCIL OF MINISTERS OF THE ENVIRONMENT, "Canadian water quality guidelines for the protection of aquatic life: Total particulate mattter.," Canadian environmental quality guidelines, 1999, 2002.
[25]
A. Simon, A. Curini, S. D. and E. Langedoen, "Streambank Mechanics and the Role of Bank and Near-Bank Processes in Incised Channels," in Incised River Channels - Processes, Forms, Engineering and Management, West Sussex, England, John Wiley & Sons Ltd, 1999, p. 442.
[26]
K. Brown, M. AUST and K. MCGUIRE, "Sediment delivery from bare and graveled forest road stream crossing approches in the Virginia Piedmont," Forest Ecology and Management, 2013.
[27]
S. e. a. Mickovski, "Simulation of direct shear tests on rooted and non-rooted soil using finite element analysis," Ecological Engineering 37 (2011) 1523– 1532, 2011.
"Wikipedia - 2013 Alberta floods," [Online]. Available: https://en.wikipedia.org/wiki/2013_Alberta_floods. [Accessed 30 03 2018].
[2]
"USDA - Natural Resources Conservation Service," [Online]. Available: https://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/technical/?cid=nrcs143_014199. [Accessed 22 March 2018].
[3]
City of Calgary, "Design guidelines for erosion and flood control projects for streambank and riparian stability restoration," 2012.
[4]
Government of Alberta - Transportation, "Erosion and sediment control manual," June 2011. [Online]. Available: http://www.transportation.alberta.ca/4626.htm.
[5]
USDA/NRCS, Streambank soil engineering - Technical supplement 14I - Part 654 (Stream restoratio design) of National Engineering Handbook, USA, 2007.
[6]
A. Stokes, J. Norris, L. Van Beek, T. Boggard, E. Camerrat, S. Mickovski, A. Jenner, A. Di Iorio and T. Fourcaud, "How vegetation reinforces soil on slopes," in Slope stability and erosion control: ecotechnological solutions, Springer, 2008, p. 290.
[7]
D. Gray and R. Sotir, Biotechnical and soil bioengineering - slope stabilization - a practical guide for erosion control, NEW YORK: John Wiley & Sons, Inc., 1996.
[8]
N. J. Coppin and I. G. Richards, Use of Vegetation in Civil Engineering, London: CIRIA, 1990.
[9]
F. Giadrossich, M. Schwarz, D. Cohen, A. Cislaghi, V. C., H. T., C. Phillips and A. Stokes, "Methods to measure the mechanical behaviour of tree roots: A review," 2017.
[10]
H. Schiechtl, Bioengineering for land reclamation and conservation, MUNICH: UNIVERSITY OF ALBERTA, 1980.
[11]
D. Polster, "Natural processes and restoration of drastically disturbed sites," Polster Environmental Services LTD., 2015.
[12]
H. Chang, Fluvial Processes in River Engineering, 1988.
[13]
N. Bankhead, R. Thomas and A. Simon, "A combined field, laboratory and numerical study of the forces applied to, and the potential for removal of, bar top vegetation in a braided river," Earth Surf. Process. Landforms 42, 439–459 (2017), 2017.
[14]
M. Da Liu and R. Williams, "Flow Hydrodynamics across Open Channel Flows with Riparian Zones: Implications for Riverbank Stability," Water, 2017.
[15]
E. Yager and M. Schmeeckle, "The influence of vegetation on turbulence and bed load transport," JOURNAL OF GEOPHYSICAL RESEARCH: EARTH SURFACE, VOL. 118, 1585–1601, 2013.
[16]
N. Pollen and A. Simon, "Estimating the mechanical effects of riparian vegetaion on stream bank stability using fiber bundle model," 2005.
[17]
T. Wu, W. Mckinnell and D. Swanson, "Strength of Tree Roots and landsides on Prince of Wales Island, Alaska," 1978.
[18]
L. Waldron and S. Dakessian, "Soil reinforcement by roots: calculation of increased soil shear resistance from root properties," 1981.
[19]
T. Endo, "Effect of Tree Roots upon the Shear Strength of Soil.," 1980.
[20]
R. Hidalgo, F. Kun and H. Herrmann, "Bursts in a fiber bundle model with continuous damage," PHYSICAL REVIEW E, VOLUME 64, 066122, 2001.
[21]
S. Mickovski and P. Van Beek, "Root morphology and effects oon soil reinforcement and slope stability of young vetiver (Vetiveria zizanoides) plants grown in semi-arid climate.," 2009.
[22]
USDA - FOREST SERVICE, "Soil Bioengineering: An Alternative for Roadside Management.," 2000.
[23]
Government of Alberta, "Guide to the Common Native Trees and Shrubs of Alberta," 2014.
[24]
CANADIAN COUNCIL OF MINISTERS OF THE ENVIRONMENT, "Canadian water quality guidelines for the protection of aquatic life: Total particulate mattter.," Canadian environmental quality guidelines, 1999, 2002.
[25]
A. Simon, A. Curini, S. D. and E. Langedoen, "Streambank Mechanics and the Role of Bank and Near-Bank Processes in Incised Channels," in Incised River Channels - Processes, Forms, Engineering and Management, West Sussex, England, John Wiley & Sons Ltd, 1999, p. 442.
[26]
K. Brown, M. AUST and K. MCGUIRE, "Sediment delivery from bare and graveled forest road stream crossing approches in the Virginia Piedmont," Forest Ecology and Management, 2013.
[27]
S. e. a. Mickovski, "Simulation of direct shear tests on rooted and non-rooted soil using finite element analysis," Ecological Engineering 37 (2011) 1523– 1532, 2011.